Refiners such as those noted above are used for refining material containing fiber. The refiner generally comprises refining members in the form of disks which rotate in relation to each other and between which the material for refining passes from the inner periphery of the refining members, where the material is supplied, to the outer periphery of the refining members, through a refining gap formed between the refining members. Often one of the refining disks is fixed whereas the other rotates. The refining disks are generally constructed from segments provided with bars on their surface. The inner segments can then have a coarser pattern and the outer segments a finer pattern in order to produce fine refining of the material.
To ensure high quality when refining material containing fiber, the disturbances in operating conditions that continually occur for various reasons must be corrected by constant control of the various refining parameters to optimum values. This can be achieved by altering the supply of water, for instance, so that a larger or smaller cooling effect is obtained, by changing the flow of material for refining, by adjusting the distance between the refining members, or by a combination of these measures. Accurate determination of the energy transferred to the material for refining, and also of the distribution of the energy over the surface of the refining members, are necessary to enable the necessary adjustments and corrections to be performed.
To determine the energy/output transferred to the material for refining, it is known to try to measure the shear forces appearing in the refining zone. What is known as a shear force occurs when two surfaces move in relation to each other with a viscous liquid between the surfaces. Such a shear force is also created in a refiner used for refining wood chips mixed with water. It may be imagined that the chips of wood are both sheared and rolled between the refining discs, as well as colliding with each other and with the bars. The shear force is caused, inter alia, by the combined force of the discs and by the coefficient of friction. The normal force exerted on the surface also varies with the radius.
As shown in Swedish Patent Application No. 504,801, a measuring device is known comprising a special sensor bar, i.e. a bar provided with sensors which sense the load exerted on the sensor bar during refining, at a number of measuring points along the bar. However, the drawback of this arrangement is that measuring is only performed on occasional bars, and the result is therefore unreliable. Furthermore, the type of transducer, or strain gauge, used in bar experiments have a short service life since the transducers are located close to the refining surface and the material used to screen the transducers from steam and pulp is subjected to an extremely demanding environment. However, despite these drawbacks, strain gauges must be used because of the design of this measuring device.
One object of the present invention is to solve the problems mentioned above and, first of all, to provide a method and a measuring device that produces a more reliable result than previously known devices, and also to provide a device with potential for a longer service life than previously known devices, thus making it more economical.